In the field of semiconductor manufacturing equipment and other fields, various processes are carried out in inner compartments in which a vacuum state or a predetermined reduced-pressure state is maintained. In the case that rotational driving power for processing operations is introduced from a motor arranged in the atmosphere on the outer side of the inner compartment, a shaft that passes through the partition wall of the compartment and extends from the atmosphere side to the vacuum side must be reliably sealed. A contactless magnetic fluid seal is known as such a sealing mechanism.
A magnetic fluid seal and a magnetic sealing unit that has a configuration in which a magnetic fluid seal is incorporated into the AC servo motor appear in Non-patent Document 1. There is a need to modify the specifications for existing AC servo motor flanges and the like and newly redesign such a built-in form of magnetic sealing unit.
In the case that existing AC servo motors are used without modification, e.g., in the case that a hollow-type existing AC servo motor is used without modification as it appears in Non-patent Document 2, there is a need to couple the rotational component of the vacuum side and the motor shaft on the atmosphere side via a coupler having a configuration that is sealed by a magnetic fluid seal. However, in this case, the rotational position of the rotational output shaft cannot be controlled with a high degree of precision due to the twisting and slipping or the like of the coupler.